Two antiregime demonstrators died in clashes in Yemen's southern port of Aden Wednesday, triggering pledges by protest leaders there that they would ratchet up pressure on longtime President Ali Abdullah Saleh.

The deaths were the first amid a series of recent protests that have rocked Yemen, initially triggered by Arab revolts in Tunisia and Egypt. The country's relatively powerful opposition parties led tens of thousands of demonstrators in consecutive Thursday rallies in the capital San'a earlier this month, calling for...